Better get it under control before you get the BTA, I killed mine within 3 days with high phosphates. Learn from my mistakes, if you could hold off on the Bta till its under control the better.
I also used a product called phosban, there like sponges, put them in the filter or float in the sump, in 5 days take it out add a new one.
Also water changes. Many of them, ive been doing them twice a week now, and my phosphate is only just now coming down.
Last but not lease, figure out where its coming from, Over feeding, bad top off water, ect....